Process for treating sclerenchyma fibers, in particular flax

ABSTRACT

A process for sclerenchyma fibers, in particular flax, includes mechanical treatment accompanied by formation of a fiber strip and alignment of the fibers essentially parallel to one another. The fibers of the fiber strip are freed of wood constituents, greases, pectins and other impurities by a chemical and/or cooking treatment of the fiber strip. The treated fiber strip is dried and then divided into shorter sections. These sections are at least partly pulled apart or opened to form fiber bundles. The fiber bundles are carded at a set moisture content of at least 10%-wt. and combined to give a fine fiber strip.

TECHNICAL FIELD

The invention generally relates to a process for the treatment ofsclerenchyma fibers, in particular flax. More particularly, thisinvention relates to mechanical treatment of sclerenchyma fibersaccompanied by formation of a fiber strip and alignment of the fibersessentially parallel to one another.

BACKGROUND OF THE INVENTION

In known processes of this type (DE-B-3 414 437) the treatment takesplace through mechanical scutching and hackling, i.e. beating andcombing of the fibers. More specifically, the flax fibers are clampedand then treated by means of hackling combs with the result that woodconstituents and the like are removed while the fibers are alignedparallel to one another. The bast is then divided into long fibers,which are kept clamped and aligned in parallel, and into so-called tow.The tow consists of very short fibers which are combed out of theclamped long fibers and removed.

From the combined long fibers, a yarn is usually produced in subsequenttreatment steps. The yarn is then processed, for example, to formtextile materials. The long fibers continue to contain wood constituentsand other impurities to a certain extent, in particular beingunbleached.

The long fibers produced by hackling cannot be mixed with short fibersof other materials, say cotton, to form mixed yarns. This is because themachines used for wet spinning of long fibers cannot process such afiber mixture, in addition to these machines working very slowly. Thelong fibers are therefore processed without the addition of other fibersto form a roving or finished yarn. The roving, which has acquired acertain strength and fiber adhesion through a first spinning step, isusually cleaned and bleached. In comparison, a cleaning of the finishedyarn is more difficult because the cleaning liquor penetrates thefinished yarn much more poorly than the roving.

The tow produced during the treatment by hackling is either directlyprocessed to form relatively coarse yarns or carded in such a way thatshort fibers form (so-called cottonizing). The short fibers are usedunbleached for the manufacture of yarns or fleeces. If the tow issubjected to a washing and bleaching process, such as flock or batchcooking, a mass of cleaned and bleached short fibers forms. This mass,however, is very matted, and in some cases the fibers are twisted orentwined with one another. It is therefore not possible to directlyproduce from this mass a fiber structure that can be processed furtherto make filaments, other than through strong mechanical tearing.However, such tearing leads to substantial waste and to fibershortening.

It is also already known (DE-A-3 923 498) to delignify and prepare flaxby passing it through mechanical treatment stations in several steps.The flax fibers, which have already been mechanically pre-treated, arebrought into a degree of parallel alignment with the help ofneedle-bearing conveyor belts. The treated and aligned fibers are thenstacked via other conveyor belts to give a fiber hank.

The fiber hank obtained in this way contains a mixture of long fibersand short fibers, in addition to still containing wood constituents andother impurities. The fibers, aligned in longitudinal direction andparallel to one another, initially have practically no bond whatsoeverwith one another. This is because the needles of the conveyor belts allcirculate in the same direction and at essentially the same rate offeed, thus merely aligning the neighboring flax fibers in the directionof feed without forming a bond between neighboring fibers. This bond isachieved only by following conveyor belts which, in addition to theirfeed motion, also create a degree of cross movement of the flax fibers,thereby intending to form fiber bundles. However, this does not resultin a noteworthy bonding of neighboring fibers.

It is also known (DE-A-1 927 043) to collect wool to form a fiber stripwhich is then subjected to a steam treatment to remove grease that ispresent. This steaming can take place during various stages of thetreatment of the fiber strip. This treatment process usually includesstretching operations, but can also include brushing and combing, toobtain a fiber strip which can be processed to give a wool yarn.However, such a process is not suitable for the preparation ofsclerenchyma fibers, in particular flax, because the sclerenchyma fiberspresent in the fiber strips produced by customary treatment processesare too stiff and not fine enough.

SUMMARY OF THE INVENTION

The object of the invention is to provide a process in whichsclerenchyma fibers, in particular flax fibers, are treated so thatfinal fibers are obtained which are comparable to cotton fibers in termsof their structure and their properties. Such comparable fibers can thenbe correspondingly processed.

A process in accordance with the present invention is developed in sucha way that the fibers of the fiber strip are freed of wood constituents,greases, pectins and other impurities by a chemical and/or cookingtreatment of the fiber strip. The treated fiber strip is dried, and thefiber strip is then divided into shorter sections. The sections are atleast partly pulled apart to form fiber bundles, and the fiber bundlesare then carded at a set moisture content of at least 10%-wt. andcombined to give a fine fiber strip.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will hereinafter bedescribed in conjunction with the drawings, wherein:

FIG. 1 is a diagram showing the fiber length distribution for fibersproduced in the Example; and

FIG. 2 is a diagram showing the fiber length distribution for cottonfibers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The practice when processing sclerenchyma fibers, in particular flaxfibers, has for decades, if not centuries, been to subject the finishedyarn or at least the roving to the cleaning step. Surprisingly, it hasbeen shown the fiber strip can be subjected to a conventional cleaningoperation without dissolution of the fiber bond. Moreover, the fibershold together even when the fiber strip is wet and retain their alignedposition.

When applying such a process step to a fiber strip made from wool or thelike, there is a further treatment of the fiber strip for processing togive a yarn, i.e. stretching operations and smoothings usually takeplace. With the process according to the invention the treated fiberstrip is divided into smaller sections, such a division beingpractically possible only if the fiber strip was dried beforehand.

The division into shorter sections can take place through cutting orthrough tearing of the fiber strip. Cutting has the advantage that it ismore easily carried out and produces precisely defined section lengths.However, cutting results in a relatively large portion of very shortfiber pieces which are not suitable for further processing. On the otherhand, tearing the fiber strip into shorter sections is somewhat moreexpensive and leads to section lengths which are not precisely defined.However, tearing does have the advantage of reducing the portion offiber pieces that are destroyed, i.e., those fibers no longer capable ofbeing further processed because of their small length.

The fibers inside the produced sections are in an essentially parallelalignment, and the fiber bundles forming the sections are at leastpartly pulled apart. That is, they are subjected to an operation whichis called "opening" in cotton processing. In cotton processing, this"opening" or "pulling apart" takes place inside a layer of cotton whichwas previously peeled off from a cotton bale.

If the fiber bundles are in a standard climate, a moisture content of9%-wt. results (the term "%-wt." refers to the weight of water relativeto the total weight of the fiber material, which is water plus solids).To separate the fibers essentially into elementary fibers during thesubsequent carding, a somewhat higher moisture content must beestablished. In particular, a moisture content between 10%-wt. and30%-wt. is established, upwardly limited by the processability on thecard. Preferably, the moisture content is between 11%-wt. and 17%-wt.,even more preferably between 12%-wt. and 14%-wt., and in a particularlypreferred embodiment 13%-wt. As a result of the increased moisturecontent, the hydrogen bridges keeping the fibers together dissolvewithout the fibers sticking in the card. The fibers produced in thisway, when combined to give a fine fiber strip, have a structuresurprisingly similar to cotton if they are flax fibers. The fine fiberstrip can then be further processed in the same way as cotton fibers,say by spinning to obtain a yarn.

The length of the sections to be manufactured from the fiber strip isessentially determined by the ability of the card used to process longfibers. The longer the sections chosen, the lower the fiber losses. Thelength preferably lies between 50 mm and 250 mm, and in particularbetween 65 mm and 120 mm. The setting of the moisture content of thefiber bundles for the carding can take place in a particularlyadvantageous way by setting the moisture content of the fiber stripappropriately prior to the division into smaller sections.

It is also possible to color the fiber strip after the cleaning by achemical and/or cooking treatment. Therefore, it becomes possible to mixfiber bundles of sclerenchyma fibers, in particular flax fibers, ofdifferent colors with one another to obtain a fine fiber strip which ismottled by the differently colored fibers.

More importantly, the process makes it possible to mix sclerenchymafibers, in particular flax fibers, with other types of fiber, e.g., woolor cotton. This was not previously possible if it was desired to obtaina cleaned yarn from such a mixing operation and further processing. Forexample, sclerenchyma fibers (in particular flax fibers) can be cleanedonly by a very different cleaning process than wool, and the chemicalsof the cleaning processes have a harmful effect on the other type offiber. Previously, however, flax fibers could be cleaned only veryinadequately when in a state broken down into short fibers. As mentionedabove, the tow consisting of short fibers is transformed by a washingand bleaching operation into a mass of fibers which are very matted and,in some cases, twisted and entwined with one another. Because of thismatting and twisting, the mass can be further processed only verypoorly. Therefore, the cleaning of the flax fibers has previously beencarried out only when these were present in the form of a half-yarn oryarn.

The fiber bundles produced according to the present invention consist ofcleaned sclerenchyma fibers, in particular flax fibers. These cleanedand spinnable fibers can be mixed with similarly cleaned wool or cottonfibers, then combined by carding to give a fine fiber strip, and finallyprocessed to give a mixed yarn. The wool or cotton fibers are usuallyadded while dry because the problem of the dissolution of hydrogen bondsduring the carding does not exist with them.

The flax fibers produced according to the invention have roughly thesame abrasion properties as synthetic fibers currently used for themanufacture of mixed yarns comprising synthetic fibers and wool orcotton. The flax fibers produced according to the invention cantherefore form a replacement for the synthetic fibers used at present.

EXAMPLE

Flax tow (bast fiber bundle) customary in the trade was parallelized ona Mackie carding machine and freed of all but 5% of the woodconstituents present in the flax tow. The continuous fiber stripobtained was laid out in a width of ca. 3 cm.

The fiber strip obtained was conducted in two passes at a speed of 5m/min through a continuously operating unit from Construzione MachineTessile, Schio, Italy. The unit has a card sliver transfer station with16 card slivers, an assembly comprising Foulard (chemicals impregnationapparatus) and intermediate steamer, a depositing steamer, 4 screeningdrum machines (Lisseuse washes), a screening drum drier and a card cancoiler.

In the first pass, an impregnation took place in the assembly comprisingFoulard and intermediate steamer at 60° C. and a pressure of 2 psi aboveatmospheric (=13.7895 kPa) with a wash solution consisting of:

35 ml/l NaOH 50 °Be

6 g/l Cottoclarin OJ (wetting agent surfactant)

3 g/l Securon 540 (complexing agent)

2 g/l Defindol EN (deaerator)

[the agents used are products of Henkel KGaA, Dusseldorf].

The pass took place at speed setting PIV, position "C 2", and the liquorabsorption was 72%. The treated fiber strip was then treated in thedepositing steamer for 30 minutes with saturated steam of 102° C. Dryingtook place at 140° C. to 150° C.

The thus-treated fiber strip was conducted through the same unit forbleaching. The bleaching took place in the assembly comprising Foulardand intermediate steamer at 20° C. and at a pressure of 2 psi aboveatmospheric (=13.7895 kPa) with an impregnating agent consisting of:

0.15 g/l magnesium sulphate

8 ml/l water glass 38 °Be

5 ml/l sodium hydroxide solution 50 °Be

6 g/l Cottoclarin OK

2 g/l Securon 540

2 g/l Belsoft 200 (plasticizer)

60 ml/l hydrogen peroxide 35%

The speed setting was the same as in the previous washing operation, andthe liquor absorption was 71%. The treatment in the depositing steamertook place under the same conditions as during the washing process. Thefiber strip was then dried at 140° C. to 150° C. and at a rate of 5m/min to a residual moisture of ca. 10%. The thus-obtained fiberstrip(s) were cut on a staple fiber cutting machine type NMC 290 fromNeumag Neumunstersche Maschinenund Anlagenbau GmbH, Neumunster, to formsections 77 mm long.

The 77 mm-long sections were passed through a card, displayingsemi-flexible packing, from Trutzschler GmbH & Co. KG, Monchengladbach,for further processing. Prior to the carding operation, in order toimprove the fiber-to-fiber adhesion in the spraying process, a finishwith 1% melt KB 109/2 and 1% adhesion promoter Silkol HV 86 from HenkelKGaA, Dusseldorf, was applied. A residual moisture of between 10% and13% was maintained during the carding operation.

Referring now to FIG. 1, the dimensions of the thus-obtained fibersagreed largely with the dimensions of cotton fibers. In particular, theobtained portions of fiber lengths for 10 drawn samples are shown in thefiber diagram. The portion of fibers having at least the length given onthe abscissa, i.e., equal to the given length or longer, is plotted onthe ordinate. As is immediately seen, this fiber length distribution isessentially the same as a fiber length distribution of cotton, as isrepresented in the fiber diagram of FIG. 2. Moreover, the fiberthickness of the obtained flax fibers was, as an examination under themicroscope shows, of the same order as the fiber thickness of the cottonfibers.

It will be understood that the above description is of preferredexemplary embodiments of the invention, and that the invention is notlimited to the specific embodiments shown. Modifications may be made inthe embodiments described herein without departing from the scope of thepresent invention as expressed in the appended claims.

I claim:
 1. A process for treating sclerenchyma fibers by mechanicaltreatment accompanied by formation of a fiber strip and alignment of thefibers essentially parallel to one another, comprising:treating thefiber strip by a chemical or cooking treatment to free the fibers ofwood constituents, greases, pectins and other impurities; drying thetreated fiber strip; dividing the fiber strip into shorter sections;pulling the sections at least partly apart to form fiber bundles; andcarding the fiber bundles, the fiber bundles having a set moisturecontent of at least 10%-wt., and combining the fiber bundles to form afine fiber strip.
 2. The process of claim 1, wherein the sclerenchymafibers comprise flax.
 3. The process of claim 1 wherein the dividingstep comprises cutting the fiber strip into shorter sections.
 4. Theprocess of claim 1, wherein the dividing step comprises tearing thefiber strip into shorter sections.
 5. The process of claims 1, whereinthe dividing step comprises manufacturing sections of a length between50 mm and 250 mm.
 6. The process of claim 5, wherein the dividing stepcomprises manufacturing sections of a length between 65 mm and 120 mm.7. The process of claim 1 further comprising treating the fiber strip toset the moisture content prior to the division step.
 8. The process ofclaim 1, wherein the maximum moisture content is 30%-wt.
 9. The processof claim 1, wherein the moisture content is between 11%-wt. and 17%-wt.10. The process of claim 9, wherein the moisture content is between12%-wt. and 14%-wt.
 11. The process of claim 1, further comprising dyingthe treated fiber strip.
 12. The process of claim 11, furthercomprising, prior to the carding step, mixing the fiber bundles withfiber bundles made from the same material but having a different color.13. The process of claim 1, further comprising, prior to the cardingstep, mixing the fiber bundles with fibers of another material.
 14. Theprocess of claim 13, further comprising using wool or cotton fibers asthe fibers of another material.
 15. The process of claim 14, furthercomprising using the wool or cotton fibers while dry.
 16. The process ofclaim 1, further comprising spinning the fine fiber strip to obtain ayarn.
 17. The process of claim 1, wherein the drying step furthercomprises drying the treated fiber strip to a moisture content in therange of 10 to 30%-wt.
 18. A yarn containing sclerenchyma fibers, theyarn made by the process of claim 1.